This application is a 35 U.S.C. xc2xa7371 national phase of PCT/IE99/00112, filed on Nov. 8, 1999, which claims priority to Irish Application Serial No. S980914, filed Nov. 6, 1998.
The present invention relates to apparatus and a method for relieving dyspnoea, and in particular, though not limited to apparatus and a method for relieving dyspnoea in an ambulatory subject, and more particularly, though not limited to an exercising ambulatory subject.
Subjects who suffer from respiratory disorders such as chronic obstructive pulmonary disease often suffer from dyspnoea or breathlessness. This is particularly so in exercising subjects. The term xe2x80x9cexercisingxe2x80x9d is used in this specification, in general, to include activities beyond the resting state, for example, the act of walking, ascending a stairs, or the like. Dyspnoea and the fear of a spell of dyspnoea create great anxiety in such subjects, and can severely limit their ability to perform even the most simple tasks, such as walking a relatively short distance, or ascending a stairs within a house. Apparatus for relieving dyspnoea in ambulatory subjects are known, although they suffer from limitations. Typically, such apparatus are portable and may be worn or carried by the subject. Typically, they provide a supply of air to a mouthpiece, a nasal mask or a face mask to be worn by the subject, and the air pressure is at a pressure greater than ambient pressure. In general, a housing which houses a blower motor is worn or carried by the subject, and a communicating conduit delivers air from the blower motor to the mouth piece or mask at the pressure greater than ambient. Typically, a controller is provided within the housing for controlling the air blower for varying the pressure at which the air is supplied to the mouthpiece for the subject. A control knob on the housing facilitates selection by the subject of the pressure at which the air is to be supplied, similarly controlled non-portable apparatus are also known.
While such apparatus are satisfactory for a subject who, for example, is resting, or alternatively is exercising at a relatively constant rate by, for example, walking at a constant rate, they are unsatisfactory where the rate of exercising by the subject is varying, for example, in the case of a subject walking from a downstairs room to an upstairs room in a house. While the subject is walking on level ground the exercise rate is at one level, however, when ascending the stairs, the exercise rate significantly increases. As the exercise rate increases the subject breathes faster. Faster breathing shortens the breathing cycle, and in particular, the expiratory part of the breathing cycle. By shortening the expiratory part of the breathing cycle less time is available for the lungs to empty. Since generally, ones lungs empty exponentially the shortened expiratory part of the cycle leads to a higher intrinsic positive end-expiratory pressure which is the pressure in the breathing cycle at which expiration ends and the subject commences the inspiratory part of the breathing cycle. Breathing being under the control of the nervous system is relatively oblivious to the mechanics of the operation of the lungs and their state of emptiness during a breathing cycle. Thus, as the intrinsic positive end-expiratory pressure increases over a number of breathing cycles as a result of increase in the exercise rate, known apparatus are unable to cope with the increased exercise rate. Similar problems may arise in the case of a resting subject should an event or crisis occur which causes an increase in the breathing rate of the subject.
There is therefore a need for apparatus and a method for relieving dyspnoea in a subject which overcomes these problems.
The present invention is directed towards providing such a method and apparatus.
According to the invention there is provided apparatus for relieving dyspnoea in a subject, the apparatus comprising an air supply means for providing an air supply at a pressure greater than ambient for delivery to the subject, wherein the apparatus further comprises a monitoring means for monitoring at least a part of at least one breathing cycle of the subject for determining the intrinsic positive end-expiratory pressure of a breathing cycle of the subject, and a control means responsive to the monitoring means for controlling the pressure of the air supply delivered to the subject at a pressure substantially matched to the intrinsic positive end-expiratory pressure.
In one embodiment of the invention the control means controls the pressure of the air supply delivered to the subject at the pressure substantially matched to the intrinsic positive end-expiratory pressure for a period at least at the end of the expiratory part of each breathing cycle.
In another embodiment of the invention the control means controls the pressure of the air supply delivered to the subject at a pressure greater than the intrinsic positive end-expiratory pressure during at least a part of the inspiratory part of each breathing cycle.
In a further embodiment of the invention the control means controls the pressure of the air supply delivered to the subject at the pressure substantially matched to the intrinsic positive end-expiratory pressure during the expiratory part of each breathing cycle.
In a still further embodiment of the invention the control means controls the pressure of the air supply delivered to the subject at a pressure greater than the intrinsic positive end-expiratory pressure during the inspiratory part of each breathing cycle.
In one embodiment of the invention the monitoring means monitors a plurality of breathing cycles, and a computing means is provided for determining the average intrinsic positive end-expiratory pressure over the said plurality of breathing cycles.
In another embodiment of the invention the monitoring means monitors each breathing cycle over the complete breathing cycle.
Preferably, the monitoring means is adapted for locating adjacent the mouth of the subject.
In one embodiment of the invention the monitoring means is adapted for locating in a mouthpiece, a nasal mask or a face mask or adjacent thereto through which the air supply is delivered to the subject .
In another embodiment of the invention signals are relayed from the monitoring means to the control means.
In one embodiment of the invention the monitoring means is connected to the control means by hard wiring.
Alternatively, a means for transmitting an airborne signal from the monitoring means to the control means is provided, and a receiving means is provided in the control means for receiving the airborne signal transmitted from the monitoring means.
Preferably, the monitoring means is a pressure transducer for monitoring the pressure of air during the breathing cycles.
Advantageously, the apparatus comprises a mouthpiece, nasal mask or a face mask, and a communicating means for communicating the mouthpiece or mask with the air supply means.
In one embodiment of the invention an exhaust means is provided in the mouthpiece or mask for exhausting exhaled air from the subject, and preferably, a valving means is provided in the exhaust means of the mouthpiece or mask, the valving means being operable under the control of the control means in response to the monitoring means for controlling the pressure of the air supply in the mouthpiece.
In a still further embodiment of the invention the valving means is a pressure regulating valving means.
In another embodiment of the invention the air supply means is operable under the control of the control means in response to the monitoring means for controlling the pressure of the air supply delivered to the subject.
In one embodiment of the invention the apparatus is portable and is adapted for use by an ambulatory exercising subject.
Ideally, the apparatus comprises a housing defining a hollow interior region, the air supply means being located within the hollow interior region. Preferably, the control means is located within the hollow interior region of the housing. Advantageously, a power source is located in the hollow interior region.
In one embodiment of the invention an air inlet and an air outlet are provided to and from the hollow interior region and the air supply means is located intermediate the air inlet and the air outlet.
Preferably, a first air filtering means is located adjacent the air inlet upstream of the air supply means, and preferably, a second air filtering means is located adjacent the air outlet of the air supply means.
Advantageously, the air outlet is adapted for receiving the communicating means.
In one embodiment of the invention a strap is provided for securing the housing to the subject.
In another embodiment of the invention a retaining means is provided on the strap for retaining the mouthpiece or mask releasably secured to the strap when not required.
In a further embodiment of the invention a receiving means is provided on the strap for receiving the communicating means. Preferably, the receiving means is a releasable receiving means for releasably receiving the communicating means.
In a further embodiment of the invention the communicating means comprises an elongated communicating conduit.
Advantageously, the communicating means comprises an elongated flexible communicating conduit.
Ideally, the communicating conduit is of concertina type construction for facilitating flexing of the conduit and storing of the conduit.
In another embodiment of the invention the control means comprises the computing means.
In a further embodiment of the invention the air supply means comprises an air blower motor. Preferably, the air blower motor is electrically powered. Advantageously, the air blower motor comprises an impeller driven by a motor.
In one embodiment of the invention the pressure at which the air supply is delivered to the subject when the pressure of the air supply is matched to the intrinsic positive end-expiratory pressure is substantially similar to the intrinsic positive end-expiratory pressure of the subject monitored by the monitoring means.
Additionally the invention provides a method for relieving dyspnoea in a subject, the method comprising the steps of providing an air supply means for delivering an air supply to the subject at a pressure greater than ambient, wherein the method further comprises monitoring at least a part of at least one breathing cycle of the subject for determining the intrinsic positive end-expiratory pressure of the subject, and controlling the pressure of the air supply to the subject so that the pressure of the air supply delivered to the subject is substantially matched to the intrinsic positive end-expiratory pressure.
In one embodiment of the invention the pressure of the air supply delivered to the subject is controlled at the pressure substantially matched to the intrinsic positive end-expiratory pressure for a period at least at the end of the expiratory part of each breathing cycle.
In another embodiment of the invention the pressure of the air supply delivered to the subject is controlled at a pressure greater than the intrinsic positive end-expiratory pressure during at least a part of the inspiratory part of each breathing cycle.
In a further embodiment of the invention the pressure of the air supply delivered to the subject is controlled at the pressure substantially matched to the intrinsic positive end-expiratory pressure during the expiratory part of each breathing cycle.
In a still further embodiment of the invention the pressure of the air supply delivered to the subject is controlled at a pressure greater than the intrinsic positive end-expiratory pressure during the inspiratory part of each breathing cycle.
In one embodiment of the invention a plurality of breathing cycles of the subject are monitored for determining the average intrinsic positive end-expiratory pressure over the said plurality of breathing cycles.
In another embodiment of the invention the complete breathing cycle of each monitored breathing cycle is monitored.
Preferably, the air pressure adjacent the mouth of the subject is monitored for determining the intrinsic positive end-expiratory pressure.
Advantageously, the air pressure is monitored in a mouthpiece, nasal mask or a face mask attached to the subject for determining the intrinsic positive end-expiratory pressure.
In one embodiment of the invention the pressure at which the air supply is delivered to the subject is at a pressure substantially similar to the determined intrinsic positive end-expiratory pressure.
In another embodiment of the invention the method is for relieving dyspnoea in an ambulatory exercising subject, and the method comprises the step of providing the air supply means as a portable air supply means.
The advantages of the invention are many. By virtue of the fact that the apparatus and method control the pressure at which the air supply is supplied to the subject at the end of the expiratory part of each breathing cycle so that the pressure of the air supply to the subject is matched to the intrinsic positive end-expiratory pressure of the subject, the subject can effectively commence inspiration immediately the expiratory part of the breathing cycle has ended. This permits maximum intake of air by the subject during the inspiration part of each breathing cycle. In other words, by virtue of the fact that the subject can commence inspiration immediately at the end of the expiratory part of the breathing cycle air can be drawn into the lungs of the subject over the entire inspiratory part of the breathing cycle. This, thus, maximises the volume of air drawn into the lungs of the subject during each breathing cycle. The matching of the pressure of the air supply delivered to the subject with the intrinsic positive end-expiratory pressure of the subject at the end of the expiratory part of each breathing cycle removes the threshold load which subjects typically encounter at the commencement of the inspiratory part of a breathing cycle. This threshold load which would otherwise be encountered by a subject is caused where the pressure of the air supply delivered to the subject is below the intrinsic positive end-expiratory pressure. Thus, by providing the air supply to the subject at a pressure matched to the intrinsic positive end-expiratory pressure at the end of the expiratory part of each breathing cycle the threshold load is eliminated.
In embodiments of the invention where the pressure of the air supply to the subject during part or all of the inspiratory part of each breathing cycle is greater than the intrinsic positive end-expiratory pressure, a further advantage is achieved in that a greater volume of air can be drawn into the lungs of the subject during the inspiratory part of the cycle.